1. Field of the Invention
The present invention relates generally to the testing of burnishing tape that is used in the fabrication of hard disks, and more particularly to methods and devices for testing the strength with which an abrasive material is bonded to the tape backing material of the burnishing tape.
2. Description of the Prior Art
Magnetic media hard disks generally include a wafer substrate having a magnetic media layer covered by a protective thin film surface layer including a diamond-like carbon (DLC) layer and a lubrication layer. A typical final step in the fabrication of such hard disks is a final burnishing of the disk surface to remove any projecting particulates and asperities from the surface of the disk, such that the finally fabricated disk has a smooth planar surface. This final burnishing step is a critical fabrication step in that the smoothness of the disk surface is a significant factor that affects the flying characteristics of a slider device which carries the read/write head of a hard disk drive. Thus, the performance of a hard disk drive is significantly influenced by the smoothness of the surfaces of its hard disks.
A typical burnishing process to which the present invention applies involves the utilization of a burnishing tape that includes a flexible backing material, such as Mylar, that has an abrasive material layer bonded to one surface. Generally, such burnishing tapes are manufactured utilizing large sheets of Mylar having smooth upper and lower surfaces. A slurry including a bonding agent and abrasive particles is applied to one surface of the Mylar sheet, and then dried and cured. Thereafter the Mylar sheet is cut into long, approximately one inch wide strips that are wound upon tape spools. One of the most significant process parameters of the burnishing tape is the bonding strength of the abrasive material layer to the Mylar tape surface. Where the bonding strength of the abrasive material to the Mylar surface is inadequate, abrasive particles can separate from the tape during the burnishing process, resulting in abrasive particulates being deposited upon the surface of the hard disks. Such delamination of the abrasive particles from the burnishing tape results in unacceptably high failure rates of hard disks, in that even a single abrasive particle resident upon the surface of a hard disk can cause a flying read/write head to crash, causing catastrophic damage to both the hard disk and the read/write head.
To solve the burnishing tape delamination problem, a method and device for testing the bonding strength of the abrasive material to the Mylar tape is required. The present invention provides such a burnishing tape testing method and device.
The method for testing burnishing tape includes placing the tape on a backing surface and applying a force normal to the abrasive surface of the tape in a localized area of the tape surface. Thereafter, an increasing pulling force is applied to the end of the tape up to a point where the tape moves under the effect of the normal force. Through prior burnishing tape product testing a known normal force N is determined and a delamination pulling force D is likewise determined, such that a burnishing tape can be said to be defective where it is placed under a normal force N and the pulling force required to move it is less than the delamination pulling force D. The values of N and D are determinable for different types of burnishing tape and thereafter utilizable to test further quantities of similar burnishing tape.
The testing device of the present invention includes a tape supporting plate, a force gauge for applying a known normal force N to the abrasive surface of the burnishing tape disposed on the plate, and a variable torque motor with a torque sensor that is utilized to apply a known variable pulling force to the tape, such that the pulling force required to move the tape under the normal force N can be determined and then compared to the predetermined delamination force D. Where the pulling force required to move the tape is less than D the tape is determined to be defective, whereas when the pulling force required to move the tape is greater than D the bonding strength of the abrasive layer of the burnishing tape is determined to be adequate such that the burnishing tape can be confidently utilized to burnish hard disk surfaces.
It is an advantage of the present invention that a method for testing burnishing tape has been developed.
It is another advantage of the present invention that a method for testing the bonding strength of the abrasive material layer of burnishing tape has been developed.
It is a further advantage of the tape burnishing test method of the present invention that the bonding strength of the abrasive layer of the burnishing tape can be measured.
It is yet another advantage of the burnishing tape testing method of the present invention that a determination can be made regarding whether abrasive particulates of the burnishing tape will delaminate from the burnishing tape during a hard disk burnishing process.
It is an advantage of the present invention that a device for testing burnishing tape has been developed.
It is another advantage of the present invention that a device for testing the bonding strength of the abrasive material layer of burnishing tape has been developed.
It is a further advantage of the burnishing tape testing device of the present invention that a roll of burnishing tape can be tested at several discrete locations throughout its length to generally determine the bonding strength of the abrasive material layer throughout the length of the tape.
These and other features and advantages of the present invention will no doubt become apparent to those skilled in the art upon reading the following detailed description which makes reference to the several figures of the drawings.